Structure and processes of formation of oxide electrocatalysts

Abstract

Catalytically active corrosion-resistant electrode coatings based on compositions of highly conductive oxides of noble metals (Ru, Ir, Pd, and Pt) and oxides of rectifying and other transition metals (Ti, Nb, Ta, Co, Ni, and Fe) [i] are widely used as low-wear anodes in important industrial electrochemical processes (production of chlorine and caustic soda, electrolysis of water to obtain hydrogen, electrolytic polishing of metals, etc.).However, in connection with the development and design of more advanced electrochemical technologies work is in progress on optimization of the properties of oxide coatings of low-wear anodes. In addition, the characteristics of the electrochemistry of oxides of these metals that have been brought to light [2,3], in comparison with the electrochemistry of the metals (Ru, Ir, and Pt), has generated interest in studying the nature and mechanism of electrocatalysis, processes of corrosion of these materials, and of course their structure and physicochemical properties. In studying the structure and electron properties of low-wear anodes attempts were made to determine correlations of the electrochemical properties with the composition and structure of crystalline phases (individual oxides or solid solutions), the microstructure (grain size of crystalline phases and imperfections), magnitude and character of true surface, the heterovalent states of the cations, and the mechanism of electrical conductivity. As a result of these investigations, it has been concluded that the oxide films of low-wear anodes obtained by pyrolysis of salts (primarily chlorides) of Ru, Ti, Ir, Sn, and Nb and deposited on the base from aqueous (alcohol) solutions are fine crystalline products of decomposition of these salts, that the imperfections of the crystallites determine the difference in the electrochemical behavior of single crystal and polycrystalline films (e.g., RuO 2 and Ir02), and that they form the basis of the effect of pyrolysis temperature on the electrochemical properties of low-wear anodes, etc.However, the studies carried out at the L. Ya. Karpov Scientific Research Institute of Physical Chemistry on the actual composition, structure and electron properties of pyrolytic ruthenium oxide and iridium oxide coatings and also two-and three-component films of composition RuO2-Ti02, IrO2-TiO 2, IrO2-RuO2-TiO 2, etc. have shown [4,5] that all these materials are products of incomplete dehydration of partially hydrated oxides of Ru, Ti, and Ir with an incomplete degree of crystallinity. These results were obtained by transmission electron microscopy and by electron and x-ray diffraction methods. The presence of molecules of H20 and OH groups in low-wear anodes was established from the data of derivatography and IR spectroscopy. For example, for ruthenium oxide films it was found that at a pyrolysis temperature of To = 450~ the coating consists of 70% crystalline phase with a rutile structure, the remainder being amorphous hydrated ruthenium oxide. Iridium oxide films obtained under the same pyr...

Surface characteristics and electrochemical corrosion behavior of NiTi alloy coated with IrO2

“…IrO 2 ·xH 2 O was crystallized with a rutile structure when the temperature was above 300°C. At temperature above 400°C, crystallites of anhydrous IrO 2 emerged [23,24].…”

Computer Simulations of the Semiconductor‐Metal Transition in Ru/Ti and Ir/Ti Mixed Oxides

“…In the case of Ag, tarnishing has been studied (4). The influence of any particular pollutant and humidity on the corrosion of Cu and Ag has been clarified to a considerable degree by testing under artificially accelerated conditions (5-7).…”